Front fork

ABSTRACT

A front fork in which a stroke amount of a spring leg that relies on an air spring can be detected precisely, wherein pressure leaks in the spring leg are detectable. The front fork has: a guide cylinder that extends from one of a vehicle body-side tube or an axle-side tube that make up a spring leg; a piston mounted to the leading end of a guide rod extending from the other one of the tubes; an inner airspring chamber in the interior of the guide cylinder; an outer airspring chamber, outward of the inner airspring chamber, in the interior of the vehicle body-side tube and the axle-side tube; first and second detectors for detecting pressure and temperature in the outer airspring chamber the inner airspring chamber, respectively; and stroke detection compensator for detecting a stroke amount on the basis of outputs of the first and second detectors.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is application claims the benefit of Japan Patent Application No.2012-123926 filed on May 31, 2012 with the Japanese Patent Office, theentire contents of which are hereby incorporated by reference in theentirety.

TECHNICAL FIELD

The present invention relates to a front fork, and more particularly, toa front fork for motorcycles in which an air spring is used as a spring.

BACKGROUND

In a conventional advance-retreat position detection device disclosed inJapanese Unexamined Utility Model Application Publication No. H3-42706and illustrated in FIG. 8, herein, focusing on the change in pressure ofa gas M1 in a chamber M2 in accordance with an advance-retreat positionof an operating member M3 in the chamber M2, the abovementioned pressureis detected by a pressure detector M4, and, thereby, the advance-retreatposition of an operation member M3 is detected by an advance-retreatposition detector M5; and focusing on the influence that hightemperature in the chamber M2 exerts on the abovementioned pressure,temperature detector M6 detects that temperature, and a temperaturecorrector M7 corrects the temperature at the advance-retreat position ofthe operation member M3 on the basis of the temperature output, so thatan accurate stroke amount is detected as a result.

Known front fork suspensions include suspensions in which front forksare disposed on the left and right, each front fork being configured inthe form of a mechanical spring and a damper integrated with each other,and also suspensions in which the functions of the spring and the damperare divided between the left and right front forks.

The springs used in front forks of the latter type include mechanicalcoil springs and air springs.

Front forks that utilize air springs are configured in the form of twoair spring chambers, namely an outer air spring chamber comprising aninner space of a vehicle body-side (first) tube and an inner space of anaxle-side (second) tube, and an inner air spring chamber that ispartitioned, from the outer air spring chamber, through sliding of apiston, which is mounted to the vehicle body-side tube, within a guidecylinder that is provided in the axle-side tube. The volume of the outerair spring chamber increases or decreases as a result of changes in thetotal length of the vehicle body-side tube and the axle-side tubeaccompanying the stroke operation of the suspension, while the volume ofthe inner air spring chamber increases or decreases as a result ofdisplacement of the piston within the guide cylinder. The air in the airspring chambers undergoes repeated compression and expansion as a resultof the abovementioned volume increases or decreases. This compressionand expansion of air translates into rises in the temperature in the airspring chambers, as well as rises in the pressure in the air springchambers on account of the increases in temperature. These rises anddrops in the pressure in the air spring chambers that accompany rises intemperature may alter the designed functionality of the air spring, andmay detract from the suspension effect in the vehicle. Therefore, itwould be conceivable, on the basis of Japanese Unexamined Utility ModelApplication Publication No. H3-42706, to measure the temperature and/orpressure in the outer air spring chamber and to use an advance-retreatposition detection device that adjusts the stroke amount according tochanges in the temperature and/or pressure.

In the advance-retreat position detection device of Japanese UnexaminedUtility Model Application Publication No. H3-42706, however, the strokeamount is detected through measurement of the pressure and temperatureof the outer air spring chamber having a greater volume than an innerair spring chamber. Accordingly, the precision of stroke detection islow. That is, the volume of the outer air spring chamber is larger thanthat of the inner air spring chamber, and hence the volume change thatarises through advance and retreat of the piston that modifies thevolume of the inner air spring chamber and the outer air spring chamberis relatively small. Therefore, pressure fluctuations are small, and thepressure and temperature changes measured by the sensors are likewisesmall. It is thus found that detection precision of the stroke amount isnot very good. Further, pressure and temperature are measured in onlyone spring chamber. This was problematic in that, as a result, it wasnot possible to detect pressure leaks (air leaks) between the inner airspring chamber and the outer air spring chamber, or between the outerair spring chamber and outside air, and it was not possible to detectimmediately the occurrence of anomalies in the air tightness of theouter air spring chamber and the inner air spring chamber. The pressuredetector and the temperature detector being configured in the form ofone set alone was a further drawback, since in that case the strokeamount cannot be detected if one of the detectors malfunctions.

SUMMARY OF THE INVENTION

In the light of the above issues, it is an object of the presentinvention to provide a front fork in which the stroke amount of a springleg, of the front fork, that relies on an air spring, can be detectedwith good precision, and in which air leaks in the spring leg canlikewise be detected.

In order to solve the above problem, a front fork is providedcomprising:

a spring leg formed including an air spring and a damper leg having adamper built therein, which are disposed parallel to each other,

the spring leg including

a vehicle body-side tube, which is fixed to a vehicle body side andwhose one end is plugged, and an axle-side tube, to which an axle ismounted and whose one end is plugged, an inner periphery space beingformed by mutual insertion of the vehicle body-side tube and theaxle-side tube;

a cylindrical guide cylinder that is disposed in the inner peripheryspace, and that is extended from the plugged end of one of the vehiclebody-side tube and the axle-side tube to the inner periphery space;

a piston that is mounted to a leading end of a guide rod that extendsfrom the plugged end of the other one of the tubes, and that slides overan inner peripheral face of the guide cylinder;

an inner air spring chamber that is partitioned by the piston in theinterior of the guide cylinder;

an outer air spring chamber that is partitioned, outward of the innerair spring chamber, in the interior of the vehicle body-side tube andaxle-side tube;

a first detector for detecting pressure and temperature in the outer airspring chamber;

a second detector for detecting pressure and temperature in the innerair spring chamber; and

a stroke detection compensator for detecting a stroke amount of thespring leg, while compensating for the influence on pressure as a resultof temperature changes in the inner air spring chamber and outer airspring chamber, on the basis of outputs of the first and seconddetector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a front fork according to an exemplaryembodiment;

FIG. 2 is a configuration diagram of the front fork according to theembodiment.

FIG. 3 is a partial enlarged diagram of a spring leg according to theembodiment.

FIG. 4 is a graph illustrating reaction forces with respect to strokeamount of the spring leg according to the embodiment.

FIG. 5 is a configuration diagram of a spring leg according to anotherembodiment.

FIG. 6 is a block diagram of a spring leg according the otherembodiment.

FIG. 7 is a graph illustrating reaction forces with respect to strokeamount of a spring leg according to the other embodiment.

FIG. 8 is a schematic configuration diagram of a conventional springleg.

The present invention is explained based on embodiments of theinvention, but the embodiments do not limit in any way the inventionaccording to the scope of the appended claims. Also, not allcombinations of features explained in the embodiments are essential forsolving the problem of the present invention. The features thusencompass configurations that can be selectively adopted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments

FIG. 1 is an external-view diagram of an exemplary embodiment of a frontfork according to the present invention.

As illustrated in FIG. 1, a front suspension 1 is made up of a pair offront forks, left and right. One of the front forks comprises a springleg 2 having an air spring mechanism for supporting a vehicle body, andthe other front fork comprises a damper leg 3 having a damping mechanismthat dampens vibration arising from the operation of the spring leg 2.The left and right front forks are thus configured to have dissimilarfunctions. The spring leg 2 and the damper leg 3 are fixed to a frame Fdenoted by a virtual line (two-dot chain line), in such a manner thatthe spring leg 2 and the damper leg 3 are parallel to each other, by wayof a fixture G, called a triple prong, that enables steering of a wheel.

That is, the front forks according to the present invention are made upof the damper leg 3, having, in the fork, no built-in damper functionthat is integrated with a spring function of the vehicle body by a metalspring, as is the case in conventional instances, and of the spring leg2 having no built-in damper function, and comprising an air springinstead of a metal spring.

In the present embodiment, the tubes positioned on the axle side of thespring leg 2 and the damper leg 3 are referred to as axle-side tubes 2A,3A, and the tubes fixed to the vehicle body side are referred to asvehicle body-side tubes 2B, 3B. In the explanation below, the vehiclebody side is upper side and the axle side is the lower side.

The spring leg 2 and the damper leg 3 are made up of the axle-side tubes2A, 3A and the vehicle body-side tubes 2B, 3B, respectively, and areprovided with axle mounting sections 2C, 3C by way of which the axle ismounted to the lower ends of the axle-side tubes 2A, 3A. A wheel isdisposed between the axle mounting section 3C of the damper leg 3 andthe axle mounting section 2C of the spring leg 2. The axle 4 runsthrough the axle mounting sections 2C, 3C and the wheel, so that thewheel is rotatably fixed.

As illustrated in FIG. 2B, the damper leg 3 has a damper function alone,and has no built-in spring function of supporting the vehicle body byway of a metal spring, as in conventional instances. In the damper leg3, a damping mechanism is configured by way of the cylinder 3D thatextends from the vehicle body-side tube 3B in such a way so as to beimmersed in fork oil 3F, a specific amount of which fills the interiorof the axle-side tube 3A, such that fork oil 3F flows through an orificethat is formed in a piston 3E that is fixed to the axle-side tube 3A.

As illustrated in FIG. 2A, the spring leg 2 is made up of the axle-sidetube 2A and the vehicle body-side tube 2B that are provided so as to becapable of sliding with respect to each other. An outer air springchamber 5 and an inner air spring chamber 6 that constitute an airspring mechanism are provided in the interior of the spring leg 2.

The outer air spring chamber 5 is formed by a space that communicatesthe inner space of the axle-side tube 2A and the inner space of thevehicle body-side tube 2B. Specifically, the outer air spring chamber 5is a space formed in such a manner that at the outer periphery of theaxle-side tube 2A, a space between the vehicle body-side tube 2B and theaxle-side tube 2A is slidingly sealed by a sliding member 8, referred toas a slide metal, an oil seal 9, and a dust seal 10 that are provided inthe opening end side inner periphery of the vehicle body-side tube 2B.

The sliding member 8 comprises a cylinder, having a specific wallthickness, that fits into a recess that is provided in the innerperiphery of the opening end side of the vehicle body-side tube 2B. Thesliding member 8 slidably supports the axle-side tube 2A with respect tothe vehicle body-side tube 2B. The oil seal 9 is provided on the vehiclebody-side tube 2B, further to the opening end side of the latter thanthe sliding member 8. The oil seal 9 blocks pressure leaks from theouter air spring chamber 5 towards outside air by further sealing thegap between the inner periphery of the vehicle body-side tube 2B and theouter periphery of the axle-side tube 2A. The dust seal 10, whichprotects the oil seal 9 against intrusion of foreign matter from theouter environment, is provided on the vehicle body-side tube 2B, furthertowards the end section than the oil seal 9.

Outer air spring chamber 5 that communicates the inner space of theaxle-side tube 2A and the inner space of the vehicle body-side tube 2Bis formed by sealing of the inner periphery space of the vehiclebody-side tube 2B and the outer periphery space of the axle-side tube 2Aby way of the sliding member 8 and the oil seal 9.

The inner air spring chamber 6 is made up of a guide cylinder 11 that isprovided in the vehicle body-side tube 2B, and by a piston 12 that ismounted to the axle-side tube.

The guide cylinder 11 is a cylinder having a smaller diameter than theinner diameter of the axle-side tube 2A. The guide cylinder 11, which isprovided with a threaded section 11A on the inner periphery of one endside, is screwed to a cap bolt 13 that plugs the end section of thevehicle body-side tube 2B; as a result, the guide cylinder 11 becomesfixed to the plugged end side that is coaxial with the axis of thevehicle body-side tube 2B.

The cap bolt 13 is a stepped threaded body, shaped in the form of stepsas that are a stack of cylinders of dissimilar outer shape, asillustrated in the enlarged diagram of FIG. 3. The cap bolt 13 comprisesa large-diameter threaded section 13A that is screwed to the vehiclebody-side tube 2B, a small-diameter threaded section 13B that is screwedto the guide cylinder 11, and an end face abutting section 13C withwhich the end face of the guide cylinder 11 comes into contact. The endface abutting section 13C, which is formed between the large-diameterthreaded section 13A and the small-diameter threaded section 13B, isformed to have a larger diameter than the outer diameter of the guidecylinder 11, such that the end face abutting section 13C projects intothe inner space of the vehicle body-side tube 2B together with thesmall-diameter threaded section 13B. The outer peripheral face of theend face abutting section 13C is formed as a straight surface that hasnot been worked through threading or the like.

Therefore, the guide cylinder 11 is positioned in the middle of theinner space of the vehicle body-side tube 2B through screwing of thelarge-diameter threaded section 13A of the cap bolt 13 to the vehiclebody-side tube 2B and through screwing of the small-diameter threadedsection 13B of the cap bolt 13 to the threaded section 11A of the guidecylinder 11. One end of the guide cylinder 11 becomes plugged byabutting, against the end face abutting section 13C, the end face of theguide cylinder 11 that is screwed to the small-diameter threaded section13B.

The cap bolt 13 has an outer air pressure adjustment section 25 thatadjusts the air pressure in the outer air spring chamber 5, an inner airpressure adjustment section 26 that adjusts the air pressure in theinner air spring chamber 6, first detector 14 comprising a pressuresensor and a temperature sensor for detecting the pressure andtemperature of the outer air spring chamber 5, and second detector 15comprising a pressure sensor and a temperature sensor for detecting thepressure and temperature of the inner air spring chamber 6.

The outer air pressure adjustment section 25 and the inner air pressureadjustment section 26 are valves, exposed at an outer end face 13E ofthe cap bolt 13, that enable inflow and outflow of air between theexterior and the interior of the outer air spring chamber 5 and of theinner air spring chamber 6.

The outer air pressure adjustment section 25 runs through the outerperipheral face of the end face abutting section 13C of the cap bolt 13,and is connected by a communicating hole 27 that extends up to the outerair pressure adjustment section 25 and that communicates the outer airpressure adjustment section 25 with the outer air spring chamber 5.

The inner air pressure adjustment section 26 runs through an inner endface 13F of the cap bolt 13, and is connected by a communicating hole 28that extends up to the inner air pressure adjustment section 26 and thatcommunicates the inner air pressure adjustment section 26 with the innerair spring chamber 6.

The air pressure in the outer air spring chamber 5 and the inner airspring chamber 6 is adjusted, by the outer air pressure adjustmentsection 25 and the inner air pressure adjustment section 26, when, forinstance, the front fork is longest (full extension state), i.e. whenthe volume of the outer air spring chamber 5 and the inner air springchamber 6 is largest. In the present embodiment, the pressure-receivingarea (cross-sectional area for supporting the stroke-derived load) ofthe inner air spring chamber 6 that receives the load that accompaniesthe stroke of the spring leg 2 is set to be smaller than thepressure-receiving area of the outer air spring chamber 5. With thefront fork in a fully extended state, the air pressure in the inner airspring chamber 6 is adjusted, by way of the outer air pressureadjustment section 25 and the inner air pressure adjustment section 26,so as to be higher, by a specific pressure difference, than the airpressure in the outer air spring chamber 5. In the present embodiment,the pressure that acts on the outer air spring chamber 5 and thepressure that acts on the inner air spring chamber 6, when the frontfork is retracted, are dissimilar. Therefore, a reaction force such asthe one illustrated in FIG. 4 can be obtained by setting the airpressure in the inner air spring chamber 6 to be greater than the airpressure in the outer air spring chamber 5. The pressure-receiving areaof the outer air spring chamber 5 is greater than the pressure-receivingarea of the inner air spring chamber 6. Therefore, in a case where, theair pressure in the outer air spring chamber 5 and the air pressure inthe inner air spring chamber 6 are set to a same pressure, the airspring force that acts on the outer air spring chamber 5 is larger thanthe air spring force that acts on the inner air spring chamber 6.Accordingly, the front fork hardens, and no stroke occurs, even if thefront fork is at its longest (full extension state). Therefore, asufficient stroke amount can be achieved by setting beforehand the airpressure in the outer air spring chamber 5 to be smaller than the airpressure in the inner air spring chamber 6.

The first detector 14, which is provided so as to be exposed at theouter peripheral face of the end face abutting section 13C of the capbolt 13, detects the temperature and pressure in the outer air springchamber 5. The second detector 15, which is provided so as to be exposedat the inner end face 13F of the cap bolt 13, detects the temperatureand pressure in the inner air spring chamber 6. Signal input-outputwirings 14C, 15C that extend from the first detector 14 and the seconddetector 15 are led out of the cap bolt 13 by way of a wiring lead-outhole 13D that is formed in the cap bolt 13. The signal input-outputwirings 14C, 15C are connected to below-described stroke detectioncompensator 100, such that the pressure and the temperature detected bythe first and second detector 14, 15 are outputted to the strokedetection compensator 100.

Specifically, the spring leg 2 has, in the interior thereof, the innerair pressure adjustment section 26 for adjusting the air pressure in theinner air spring chamber 6, and the second detector 15 for measuring thepressure and temperature of the inner air spring chamber 6, and has alsothe outer air pressure adjustment section 25 for adjusting the airpressure in the outer air spring chamber 5, and the first detector 14for measuring the pressure and temperature of the outer air springchamber 5.

Returning to FIG. 2A, the piston 12 is a circular column that is mountedon the leading end of a guide rod 17 that extends from the plugged endof the axle-side tube 2A, such that the piston 12 slides along theinterior of the guide cylinder 11. The guide rod 17 comprises acylindrical hollow pipe. A threaded section that is formed on the endsection outer peripheral face of the guide rod 17, at the opposite endsection at which the piston 12 is mounted, is screwed onto a bottom bolt18 for plugging the end section of the axle-side tube 2A. The guide rod17 becomes fixed thereby to the plugged end side of the axle-side tube2A. The guide rod 17 is also provided with a through-hole 17A that runsthrough the inner peripheral face and the outer peripheral face of theguide rod 17, and that communicates the hollow space of the guide rod 17with the inner periphery space of the guide cylinder 11. As a result,the air spring effect elicited by the spring leg 2 is enhanced throughan increase in the capacity of the interior of the outer air springchamber 5 in the spring leg 2. The length of the guide rod 17 is set insuch a manner that the piston 12 does not jut out of the guide cylinder11 when the spring leg 2 is longest, and in such a manner that thepiston 12 does not hit the cap bolt 13 when the spring leg 2 isshortest.

A rebound spring 19 is disposed between the guide rod 17 and the guidecylinder 11 in a state where the piston 12 is disposed in the guidecylinder 11. The rebound spring 19 is disposed in such a manner so as tosurround the outer periphery of the guide rod 17 between the piston 12and a ring-like spring stop member 20 that is provided in the openingend side of the guide cylinder 11. Accordingly, the rebound spring 19constitutes a buffering fixture that prevents the piston 12 from hittingthe spring stop member 20 when the spring leg 2 is longest. The springstop member 20 is a guide member that is fitted or screwed to the endsection of the guide cylinder 11 and that supports the sliding of theguide rod 17.

A balance spring 21 is disposed between the guide cylinder 11 and theaxle-side tube 2A. The balance spring 21, which is a spring made up of ametal and formed to a coil shape, is interposed between a springreceiver 23 that is provided in the outer periphery of the guidecylinder 11 and a spring stop member 22 that is screwed to the endsection of the axle-side tube 2A, outside the guide cylinder 11. Thebalance spring 21 acts to retract the vehicle body-side tube 2B and theaxle-side tube 2A against the spring force of the air spring of theouter air spring chamber 5 and the air spring of the inner air springchamber 6. Specifically, the balance spring 21 is disposed to surroundthe guide cylinder 11 between the ring-like spring stop member 22 thatis provided at the opening end of the axle-side tube 2A, and the springreceiver 23 that is provided at an intermediate portion in the outerperiphery of the guide cylinder. The purpose of the balance spring 21 isto curtail sudden extension of the axle-side tube 2A on account of themomentum that arises when the axle-side tube 2A is pushed back by thereaction force of air that is compressed in the outer air spring chamber5 and the inner air spring chamber 6 when the spring leg 2 retracts.

Therefore, the outer air spring chamber 5 is formed by a space intowhich the vehicle body-side tube 2B and the axle-side tube 2A arepartitioned, outward of at least the inner air spring chamber 6, in theguide cylinder 11, such that the outer air spring chamber 5 functions asan air spring through changes in volume that arise in that space whenthe axle-side tube 2A moves with respect to the vehicle body-side tube2B. The change in volume in the outer air spring chamber 5 arising fromthe stroke of the spring leg 2 is detected on the basis of the pressureand temperature, in that space, by the first detector 14.

The inner air spring chamber 6 functions as an air spring throughchanges in the volume that is surrounded by the inner peripheral face ofthe guide cylinder 11, the piston 12 and the cap bolt 13, upondisplacement, within the guide cylinder 11 of the vehicle body-side tube2B, of the piston 12 that is fixed to the axle-side tube 2A, in responseto displacement of the axle-side tube 2A with respect to the vehiclebody-side tube 2B. Changes in volume of the inner air spring chamber 6during a stroke of the spring leg 2 are detected, on the basis of thepressure and temperature in the space, by the second detector 15.

As FIG. 3 shows, the stroke detection compensator 100 is a so-calledcomputer that is provided with a CPU as computing means, a ROM and a RAMas storage means, and an I/O interface as communications means. Thestorage means stores a processing program for detecting a stroke amount.For instance, the storage means stores a data map for calculating astroke amount on the basis of detected pressure and temperature. Thestroke amount can be easily detected with good precision thereby.

The stroke detection compensator 100 comprises an advance-retreatposition calculator 101, temperature compensator 102, pressure leakdetector 103 and stroke amount calculator 104.

The advance-retreat position calculator 101 calculates anadvance-retreat position for each of the outer air spring chamber 5 andthe inner air spring chamber 6. The advance-retreat position calculator101 calculates the advance-retreat position from a reference position ofthe axle-side tube 2A with respect to the vehicle body-side tube 2B, onthe basis of the pressure detected by the pressure sensor of the firstdetector 14, and calculates the advance-retreat position from areference position of the piston 12 with respect to the guide cylinder11 on the basis of the pressure detected by the pressure sensor of thesecond detector 15. For instance, zero is set as the reference positionwhen the front fork is longest (full extension state); as a result, thevolume of the outer air spring chamber 5 and the inner air springchamber 6 becomes largest, and the pressure value measured by thepressure sensors of the first detector 14 and the second detector 15 isdetected only as a positive value. The stroke amount can therefore beeasily detected. As regards the reference position, the position at atime where the vehicle is in a 1G state, i.e. when a person riding thevehicle has a weight as is set in the design stage, may be set to strokeamount zero. Alternatively, the position at a time where the vehicle isempty may be set to zero.

The temperature compensator 102 is means for compensating for the changein pressure, in the outer air spring chamber 5 and the inner air springchamber 6, that results from temperature changes at a time when rises ordrops from the reference temperature in the outer air spring chamber 5and inner air spring chamber 6, as detected by the temperature sensor ofthe first detector 14 and the temperature sensor of the second detector15.

For instance, when the temperature of the outer air spring chamber 5 andthe inner air spring chamber 6 rises from the reference temperature, thepressure values measured by the pressure sensors of the first and seconddetector 14, 15 result from adding the change in pressure caused bychanges in temperature in the outer air spring chamber 5 and the innerair spring chamber 6, as a result of the operation of the spring leg 2,to the change in load that actually acts on the suspension, i.e. thechange in pressure caused by changes in volume of the outer air springchamber 5 and the inner air spring chamber 6 as a result of the strokeof the spring leg 2. That is, the pressure measured by the pressuresensors of the first and second detector 14, 15 are outputted as largeror smaller, and hence the temperature compensator 102 corrects thechanges in pressure value that accompany temperature changes of air inthe outer air spring chamber 5 and the inner air spring chamber 6.

Examples of methods for implementing temperature compensation include,for instance, a method wherein the expansion rate and contraction ratethat accompany temperature changes at times where the temperature risesor drops from a reference temperature are worked out beforehand andstored in the temperature compensator 102, and the pressure value thatarises on account of temperature changes is calculated from theexpansion rate and the contraction rate, and the pressure value derivedtemperature changes is subtracted from the pressure values that aremeasured by the pressure sensors, to detect the stroke amount as aresult.

The pressure leak detector 103 works out an increase or decrease valuethat is a difference in pressure values detected by the pressure sensorof the first detector 14 and the pressure sensor of the second detector15 with respect to the set reference pressure value as a referencevalue, such that the pressure leak detector 103 detects that a pressureleak has occurred when the increase or decrease value is greater than aspecific threshold value set beforehand.

Specifically, a pressure leak is detected to have occurred between theouter air spring chamber 5 and outside air when the increase or decreasevalue of the pressure value detected by the second detector 15 withrespect to the set reference pressure value in the inner air springchamber 6 is equal to or smaller than a threshold value, and theincrease or decrease value of the pressure value detected by the firstdetector 14 with respect to the set reference pressure value in theouter air spring chamber 5 is equal to or greater than a thresholdvalue. A pressure leak is detected to have occurred between the outerair spring chamber 5 and the inner air spring chamber 6 when theincrease or decrease value of the pressure value detected by the seconddetector 15 with respect to the set reference pressure value in theinner air spring chamber 6 is equal to or greater than the thresholdvalue, and the increase or decrease value of the pressure value detectedby the first detector 14 with respect to the set reference pressurevalue in the outer air spring chamber 5 is equal to or greater than thethreshold value. As regards detected pressure leaks, the failure warningdisplay device 110, as a failure alarm, is connected to the strokedetection compensator 100, so that, as a result, it becomes possible toimmediately notify, to the rider, the occurrence of an anomaly such as apressure leak or the like in the outer air spring chamber 5 and theinner air spring chamber 6 of the spring leg 2. For instance, thefailure warning display device 110 may be a simplified display devicethat lights up with a warning light when an anomaly such as a pressureleak or the like occurs in either from among the outer air springchamber 5 and the inner air spring chamber 6 of the spring leg 2;alternatively, the failure warning display device 110 may be a displaydevice that displays in detail each site at which a pressure leak hasoccurred.

Another method for detecting pressure leaks may involve comparingpressure values detected by the pressure sensor of the first detector 14and the pressure sensor of the second detector 15, and detecting that apressure leak has occurred between the outer air spring chamber 5 andthe inner air spring chamber 6 if the pressure values are identical.

The stroke amount calculator 104 calculates, and outputs, a strokeamount in accordance with an actual load value that acts on thesuspension, on the basis of the position and pressure value calculatedby the advance-retreat position calculator 101 and the temperaturecompensator 102.

As a result, it becomes possible to calculate an accurate stroke amountaccording to the load that acts on the suspension during travel. Forinstance, an air inflow-outflow device, not shown, that enables inflowand outflow of air into and out of the outer air spring chamber 5 andthe inner air spring chamber 6, may be connected to the outer airpressure adjustment section 25 and the inner air pressure adjustmentsection 26, so that, as a result, the air pressure in the outer airspring chamber 5 and the inner air spring chamber 6 is adjusted, on thebasis of the calculated stroke amount, through inflow or outflow of airby way of the outer air pressure adjustment section 25 and the inner airpressure adjustment section 26. Stable travel of the motorcycle can becontrolled as a result.

The outer air spring chamber 5 and the inner air spring chamber 6 of thespring leg 2 according to the present embodiment exhibit reaction forcecharacteristics such as those illustrated in FIG. 4 with respect tostroke amount. The air pressure in the inner air spring chamber 6 havinga smaller pressure-receiving area than the pressure-receiving area ofthe outer air spring chamber 5 is set to be high; as a result, itbecomes possible to improve suspension start-off while maintaining theinitial reaction force of the stroke from the time of full extension ofthe front fork. The outer air spring chamber 5, where pressure is set tobe lower than the air pressure in the inner air spring chamber 6, canoperate in such a manner so as to elicit an auxiliary reaction force,from about the middle of the stroke to the back of the stroke (shorteststroke). Therefore, the pressure in the inner air spring chamber 6,where the air pressure value is high, is detected by the pressure sensorof the second detector 15, and the pressure detected by the pressuresensor is corrected on the basis of the temperature detected by thetemperature sensor of the second detector 15. The stroke amount can bedetected as a result with good precision.

The pressure and temperature in the outer air spring chamber 5 and theinner air spring chamber 6 are detected individually by the first andsecond detector 14, 15. As a result, it becomes possible to detectpressure leaks between the outer air spring chamber 5 and the inner airspring chamber 6, and between the outer air spring chamber 5 and outsideair, to detect immediately malfunction of the spring leg 2, and toafford safe running of the motorcycle.

FIG. 5 illustrates the configuration of a spring leg 2 of an alternativeembodiment, and FIG. 6 is a block diagram of the spring leg 2 of FIG. 5.

The spring leg 2 explained in the above embodiment comprises themechanical balance spring 21 and rebound spring 19, as well as an airspring that comprises the outer air spring chamber 5 and the inner airspring chamber 6. However, as illustrated in FIG. 5, the spring leg 2may be configured as comprising the air spring alone, without using amechanical spring such as the balance spring 21 and the rebound spring19. Such a configuration enables a weight reduction of the spring leg 2and accordingly a reduction of the unsprung weight. As a result, itbecomes possible to enhance conformability of the wheels to the roadsurface, and to enhance the functionality of the spring leg 2.

In a specific configuration, as illustrated in FIG. 5 and FIG. 6, thespace between the outer peripheral face of the guide rod 17 and theinner peripheral face of the guide cylinder 11 is sealed, as analternative to the spring stop member 20 that is provided at the openingend of the guide cylinder 11, and there is provided a rod guide 30 thatsupports the guide rod 17, such that a rebound air spring chamber 7 ismade up of the piston 12, the rod guide 30 and the hollow space in theguide rod 17. The balance spring 21 and the rebound spring 19 aresuperseded thereby.

The volume of the rebound air spring chamber 7 increases when the springleg 2 retracts and the piston 12 moves in such a manner that the volumein the inner air spring chamber 6 is smaller. As a result of thisincrease in volume, the pressure in the rebound air spring chamber 7 isbrought to a reduced-pressure (negative pressure) state, from areference pressure, and a force acts on the piston 12 urging the latterto return to the reference position.

Accordingly, the change in pressure (negative pressure) that occurs inthe rebound air spring chamber 7 acts to conform to the force thatcompresses the inner air spring chamber 6, even under the action of aload such that the spring leg 2 is caused to retract suddenly.Therefore, it becomes possible to prevent sudden changes in strokeamount in the spring leg 2, and to elicit an effect similar to that ofthe balance spring 21, in the above-described embodiment.

Air in the rebound air spring chamber 7 is compressed when the springleg 2 extends suddenly on account of the reaction force of the outer airspring chamber 5 and the inner air spring chamber 6 in a compressedstate. As a result there is elicited the same effect as that of therebound spring 19 of the above-described embodiment. In the explanationof the present embodiment as well, the volume of the inner air springchamber 6 is smaller than the volume of the outer air spring chamber 5.

Third detector 16 for detecting the pressure and temperature of therebound air spring chamber 7 is provided in the latter. Specifically,the third detector 16 is provided in the bottom bolt 18 that fixes theguide rod 17.

As illustrated in FIGS. 5A and 5B, the bottom bolt 18 comprises, ascylindrical threaded bodies, an outer threaded section 18A that isscrewed onto the axle-side tube 2A, and an inner threaded section 18Bthat is screwed onto the guide rod 17. The outer threaded section 18A isa threaded section that is formed on the outer periphery of the bottombolt 18, and that plugs the end section of the axle-side tube 2A bybeing screwed onto the threaded section of a bolt mounting hole that isformed on the end section of the axle-side tube 2A. The inner threadedsection 18B is formed on the inner peripheral face of a hole that isprovided along a bolt centerline, from substantially the center of abolt end face 18C. The dimension of the inner threaded section 18B islarge enough to enable screwing onto the threaded section that is formedon the end-section outer periphery of the guide rod 17.

The bottom bolt 18 is provided with a rebound air pressure adjustmentsection 32 that adjusts the air pressure in the rebound air springchamber 7, and with third detector 16 that comprises a pressure sensorand a temperature sensor for detecting the pressure and temperature inthe rebound air spring chamber 7.

The rebound air pressure adjustment section 32 is a valve, exposed atthe end face 18E of the bottom bolt 18, on a tool engagement sectionside, that enables inflow and outflow of air between the exterior andthe interior of the rebound air spring chamber 7. The rebound airpressure adjustment section 32 communicates with a through-hole 33 thatruns through the inner threaded section 18B of the bottom bolt 18. Thethrough-hole 33 communicates with the rebound air spring chamber 7 at abottom section 18D of the inner threaded section 18B.

Adjustment of the air pressure in the rebound air spring chamber 7 bythe rebound air pressure adjustment section 32 is performedsimultaneously with the adjustment of the air pressure in the outer airspring chamber 5 and the inner air spring chamber 6 by the outer airpressure adjustment section 25 and the inner air pressure adjustmentsection 26. For instance, the adjustment is performed when the frontfork is longest (full extension state), i.e. when the volume of theouter air spring chamber 5 and the inner air spring chamber 6 is largestand the volume of the rebound air spring chamber 7 is smallest. In thepresent embodiment, the pressure-receiving area of the inner air springchamber 6 is set to be smaller than the pressure-receiving area of theouter air spring chamber 5, and is set so that, with the front fork in afully extended state, the air pressure in the inner air spring chamber 6is higher than the air pressure in the outer air spring chamber 5, andthe air pressure in the rebound air spring chamber 7 is higher than theinner air spring chamber 6, by way of the outer air pressure adjustmentsection 25, the inner air pressure adjustment section 26 and the reboundair pressure adjustment section 32. As a result, it becomes possible toprevent the piston 12 from hitting the rod guide 30 when the spring leg2 of the front fork is shortest. The pressure-receiving areas of theinner air spring chamber 6 and the rebound air spring chamber 7 areidentical.

The third detector 16, which is provided exposed at the side face of thebottom bolt 18, detects the temperature and pressure in the rebound airspring chamber 7. The detection sections of the pressure sensor andtemperature sensor in the third detector 16 are exposed at thecommunicating hole 34 that communicates with the through-hole 33. Thepressure and temperature in the rebound air spring chamber 7 aredetected thereby. Wiring 16C that extends from the third detector 16 isdirectly exposed from the bottom bolt 18, and is connected to thebelow-described stroke detection compensator 100. The pressure andtemperature detected by the third detector 16 are outputted to thestroke detection compensator 100.

The outer air spring chamber 5, the inner air spring chamber 6 and therebound air spring chamber 7 in the spring leg 2 according to thepresent embodiment elicit reaction forces such as those illustrated inFIG. 7 with respect to the stroke amount. Specifically, the air pressurein the inner air spring chamber 6 having a smaller pressure-receivingarea than the pressure-receiving area of the outer air spring chamber 5,is set to be high, and the air pressure in the rebound air springchamber 7 is set to be higher than the air pressure in the inner airspring chamber 6 at the time where the volume of the inner air springchamber 6 is largest and the volume of the rebound air spring chamber 7is smallest; as a result, it becomes possible to improve suspensionstart-off while maintaining the initial reaction force of the strokefrom the time of full extension of the front fork. The outer air springchamber 5, in which pressure is set to be lower than the air pressure inthe inner air spring chamber 6 and in the rebound air spring chamber 7,can operate in such a manner so as to elicit an auxiliary reactionforce, from about the middle of the stroke to the back of the stroke(shortest stroke). Therefore, the air pressure in the inner air springchamber 6 and the rebound air spring chamber 7, where air pressure isset to be high, is detected by the pressure sensor of the seconddetector 15 and the pressure sensor of the third detector 16, and thepressures detected by the pressure sensors are corrected on the basis ofthe temperature detected by the temperature sensor of the seconddetector 15 and the temperature sensor of the third detector 16.Thereby, stroke amount can be detected with good precision.

Even for a small change in the stroke amount, the change in pressure inthe inner air spring chamber 6 and the rebound air spring chamber 7,where the initial pressure value whereof is set to be high, manifestsitself more pronouncedly than the change in pressure in the outer airspring chamber 6. Accordingly, the stroke amount can be detected, withgood precision, on the basis of the detected pressure, through detectionof the pressure in the inner air spring chamber 6 by way of the seconddetector 15 and through detection of the pressure in the rebound airspring chamber 7 by way of the third detector 16.

In the spring leg 2 according to the present invention, the initialsealing pressure of air is high, and pressure fluctuation accompanyingchanges in the stroke amount are substantial. The pressure in the innerair spring chamber 6 and the rebound air spring chamber 7 is detected bythe respective pressure sensors of the second detector 15 and the thirddetector 16, and the pressure detected by the pressure sensors iscorrected on the basis of the temperature detected by the respectivetemperature sensors of the second detector 15 and the third detector 16.The stroke amount, having undergone temperature compensation, can bedetected with good precision as a result.

The first, second and third detector 14, 15, 16 that detect pressure andtemperature are individually provided in the outer air spring chamber 5,the inner air spring chamber 6 and the rebound air spring chamber 7,respectively. Thereby, pressure leaks in the outer air spring chamber 5,the inner air spring chamber 6 and the rebound air spring chamber 7 canbe detected through individual detection of the pressure and temperaturein the outer air spring chamber 5, the inner air spring chamber 6 andthe rebound air spring chamber 7.

The pressure leak detector 103 of the stroke amount detectioncompensator 100 detects an increase or decrease value that is adifference in pressure values detected by the pressure sensor of thefirst detector 14, the pressure sensor of the second detector 15 and thepressure sensor of the third detector 16, with respect to referencepressure values set as reference values of the outer air spring chamber5, the inner air spring chamber 6 and the rebound air spring chamber 7,respectively. The pressure leak detector 103 can detect that a pressureleak has occurred when the increase or decrease value is greater than aspecific threshold value set beforehand.

Specifically, a pressure leak can be detected to have occurred betweenthe outer air spring chamber 5 and outside air when the increase ordecrease value of the pressure value detected by the second detector 15with respect to the set reference pressure value in the inner air springchamber 6 does not exceed a threshold value, and the increase ordecrease value of the pressure value detected by the first detector 14with respect to the set reference pressure value in the outer air springchamber 5 exceeds a threshold value; a pressure leak can be detected tohave occurred between the outer air spring chamber 5 and the inner airspring chamber 6 when the increase or decrease value of the pressurevalue detected by the second detector 15 with respect to the setreference pressure value in the inner air spring chamber 6 exceeds athreshold value, and the increase or decrease value of the pressurevalue detected by the first detector 14 with respect to the setreference pressure value in the outer air spring chamber 5 exceeds athreshold value; a pressure leak can be detected to have occurredbetween the inner air spring chamber 6 and the rebound air springchamber 7 when the increase or decrease value of the pressure valuedetected by the second detector 15 with respect to the set referencepressure value in the inner air spring chamber 6 exceeds a thresholdvalue and the increase or decrease value of the pressure value detectedby the third detector 16 with respect to the set reference pressurevalue in the rebound air spring chamber 7 exceeds a threshold value; apressure leak can be detected to have occurred between the outer airspring chamber 5 and the rebound air spring chamber 7 when the increaseor decrease value of the pressure value detected by the third detector16 with respect to the set reference pressure value in the rebound airspring chamber 7 exceeds a threshold value and the increase or decreasevalue of the pressure value detected by the first detector 14 withrespect to the set reference pressure value in the outer air springchamber 5 exceeds a threshold value.

The pressure leaks detected by the pressure leak detector 103 can bedisplayed, for each site at which the pressure leak has occurred, bydisplay means that is connected to the stroke detection compensator 100.As a result it becomes possible to immediately notify, to the rider,about the occurrence of an anomaly in the outer air spring chamber 5,the inner air spring chamber 6 and the rebound air spring chamber 7 ofthe spring leg 2, and to afford safe running of the motorcycle.

The inner air spring chamber 6 and the outer air spring chamber 5 areindependent from each other. Therefore, the vehicle body can besupported by the reaction force of the inner air spring chamber 6, andlow-speed travel is enabled, for a load corresponding to that of oneoccupant, even in a case of hypothetical pressure leak through loss ofair pressure in the outer air spring chamber 5 caused by damage to thetubes on account of chipping (small scratches) due to a flying stonehitting the axle-side tube 2A.

In the above explanation, the detector 14 to 16 are provided formeasuring individually the pressure and temperature inside the airspring chambers 5 to 7 that are provided in the spring leg 2, such thatthe stroke amount can be detected with high precision through detectionof the actual stroke amount, by the stroke detection compensator 100, onthe basis of the outputs of the detector 14 to 16. In particular, thedetector 14, 15, 16 are provided in the air spring chambers 5, 6, 7, inwhich the compression ratio is high and pressure fluctuation issubstantial in response to the stroke amount, such that the stroke canbe detected with higher precision than in conventional instances, byvirtue of a configuration wherein the stroke amount is detected on thebasis of the pressure and temperature that are outputted by the detector14, 15, 16. High-precision stroke detection, independent from thetemperature of the air spring chambers 5 to 7, is made thus possible,since the temperature and the pressure in the air spring chambers 5 to 7can be detected and temperature compensation can be performed for thedetected pressure. Providing individually the detector 14 to 16 in therespective air spring chambers 5 to 7 makes it possible to detectpressure leaks in the partitioned air spring chambers 5 to 7, and todetect emergencies in the spring leg 2. The air spring chambers 5 to 7are provided with the respective plurality of detector 14 to 16.Accordingly, even if any of the detector 14 to 16 are damaged, thestroke amount can still be detected, although with lower precision, bythe undamaged detector. Fine control of the vehicle body attitude ismade possible, on the basis of this high-precision detection of strokeamount, through connection of, for instance, an air pressure adjustmentdevice to the air pressure adjustment sections 25, 26, 32.

Providing the detector 14 to 16 for detecting the stroke amount in theinterior of the spring leg 2, as in the present embodiment, elicits theeffect of reducing damage to the detector, and of facilitating thearrangement of the detectors 14 to 16. The pressure and temperature ofair in the interior of the air spring chambers 5 to 7 is measuredelectrically by sensors, and the stroke amount is detected as a result.It becomes hence possible to detect the stroke amount easily and withgood precision.

In the explanation of the embodiments above, the pressure-receiving areaof the outer air spring chamber 5 that receives the load thataccompanies the stroke of the spring leg 2 is set to be larger than thepressure-receiving area of the inner air spring chamber 6. However, thepressure-receiving areas of the outer air spring chamber 5 and the innerair spring chamber 6 may be identical; alternatively, thepressure-receiving area of the outer air spring chamber 5 may be set tobe smaller than the pressure-receiving area of the inner air springchamber 6.

In a case where the pressure-receiving areas of the outer air springchamber 5 and the inner air spring chamber 6 are identical, it issufficient to set an identical air pressure for the outer air springchamber 5 and the inner air spring chamber 6 in an initial setting state(for example, in a completely stretched state). In such a case, amalfunction in the form of an anomaly of the spring leg 2 can benotified immediately, by the failure warning display device 110, ifthere arises a difference in the pressure values detected by the firstdetector 14 and the second detector 1. In a case where thepressure-receiving area of the outer air spring chamber 5 is smallerthan the pressure-receiving area of the inner air spring chamber 6, theair spring force required in the spring leg 2 can be achieved throughsetting of the air pressure in the outer air spring chamber 5 to behigher than the air pressure in the inner air spring chamber 6.

In the explanation above, the air spring chambers 5, 6, 7 of the springleg 2 have air sealed therein, but the gas is not limited to air, andmay be nitrogen or the like.

In the explanation of the embodiments above, the spring leg 2 has theguide cylinder 11 provided in the vehicle body-side tube 2B, and thepiston 12 provided in the axle-side tube 2A. However, the guide cylinder11 may be provided in the axle-side tube 2A, and the piston 12 may beprovided in the vehicle body-side tube 2B. The embodiments above havebeen explained by way of an example of an inverted suspension, butneedless to say, the invention can be used in upright suspensions.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. It is intended that the present inventioninclude such modifications and variations as come with the scope of theappended claims and their equivalents.

What is claimed is:
 1. A front fork for a motorcycle comprising: aspring leg including an air spring and a damper leg having a damperbuilt therein, the spring leg and the damper leg being disposed parallelto each other, the spring leg including a first tube, which is fixed toa body side of the motorcycle and having one end that is plugged, and asecond tube to which an axle of the motorcycle is fixed and having oneend that is plugged, an inner periphery space being formed by insertingthe second tube into the first tube; a cylindrical guide cylinder thatis disposed in the inner periphery space, and that is extended from theplugged end of the first tube to the inner periphery space; a pistonthat is mounted to a leading end of a guide rod that extends from theplugged end of the second tube, and that slides over an inner peripheralface of the guide cylinder; an inner air spring chamber that ispartitioned by the piston in an interior of the guide cylinder; an outerair spring chamber that is partitioned, outward of the inner air springchamber, in an interior of the first tube and an interior of the secondtube; a first detector for detecting pressure and temperature in theouter air spring chamber; a second detector for detecting pressure andtemperature in the inner air spring chamber; and a stroke detectioncompensator for compensating for an influence on the pressure as aresult of temperature changes in the inner air spring chamber and theouter air spring chamber and detecting a stroke amount of the springleg, on the basis of detection results of the first detector and thesecond detector.
 2. The front fork according to claim 1, wherein thespring leg further comprises: a rod guide in the guide cylinder, thatsupports the guide rod to which the piston is mounted; a rebound airspring chamber partitioned by the rod guide and the piston that isinserted in the guide cylinder; and a third detector for detectingpressure and temperature in the rebound air spring chamber, and whereinthe stroke detection compensator detects the stroke amount of the springleg on the basis of the pressures and temperatures that are outputted bythe first, second and third detectors.
 3. The front fork according toclaim 1, wherein the stroke detection compensator has a failure alarmfor indicating a malfunction of the spring leg.
 4. The front forkaccording to claim 2, wherein the stroke detection compensator has afailure alarm for indicating a malfunction of the spring leg.